Gaseous alternative fuels, such as hydrogen and natural gas, are valued for their clean burning characteristics in motor vehicle engines. A particularly clean burning gaseous alternative fuel known as HYTHANE is formed from a mixture of hydrogen and natural gas. The prefix “Hy” in HYTHANE is taken from hydrogen. The suffix “thane” in HYTHANE is taken from methane, which is the primary constituent of natural gas. HYTHANE is a registered trademark of Brehon Energy PLC. HYTEANE typically contains about 5% to 7% hydrogen by energy. Natural gas is typically about 90+% methane, along with small amounts of ethane, propane, higher hydrocarbons, and “inerts” like carbon dioxide or nitrogen.
Hydrogen and methane are complimentary vehicle fuels in many ways. Methane has a relatively narrow flammability range that limits the fuel efficiency in engine applications utilizing a dilute air/fuel mixture and super-aspiration. It is common to dilute the air/fuel mixture with either excess air or recycled exhaust gases, known as lean-burn and exhaust gas recirculation (EGR), respectively. Super-aspiration is commonly achieved with a turbocharger or other supercharging pump. The addition of even a small amount of hydrogen extends the lean flammability range significantly. Methane also has a slow flame speed, especially in lean air/fuel mixtures, while hydrogen has a flame speed about 8 times faster. Methane is a fairly stable molecule that can be difficult to ignite, but hydrogen has an ignition energy requirement about 25 times lower than methane. Finally, methane can be difficult to completely combust in the engine or catalyze in exhaust aftertreatment converters. In contrast, hydrogen is a powerful combustion stimulant for accelerating the methane combustion within an engine, and hydrogen is also a powerful reducing agent for efficient catalysis at lower exhaust temperatures.
Although pure hydrogen fuel can reduce emissions by up to 100%, in the near term there is an objectionable cost differential between fossil fuels and hydrogen. Hydrogen costs are proportional to hydrogen energy, which may be expressed as a percentage of the energy consumed by the baseline energy system (e.g., a non-hydrogen fueled vehicle). However, hydrogen costs alone do not consider the benefits provided by a hydrogen fuel system. To fully understand the benefits of using hydrogen as a fuel, a larger view of the use and economics of hydrogen is necessary.
The present invention considers the reduction in emissions by a hydrogen enriched fuel. The ratio of percent emissions reduction to percent hydrogen energy, relative to baseline conditions, is a measure of the effectiveness of hydrogen utilization called the leverage factor. Hydrogen leverage is defined as the ratio of [% Emissions Reduction]/[% Baseline Energy Supplied as Hydrogen]. For example, a fleet of 100 natural gas buses converted for operation on pure hydrogen, will have a total reduction in emission of about 7%. This means the leverage of using hydrogen is 7%/7%=1. However, the same fleet could use the same amount of hydrogen (7% by energy), blended with natural gas for all 100 buses, and achieve an emissions reduction of 50% for the entire fleet. In this case, the hydrogen leverage is 50%/7%=7.14, or over 7 times as effective as the pure hydrogen case.
The present invention also considers the complete life cycle of the fuel. For example, a biofuel such as ethanol may reduce the emissions produced by a gasoline engine. However, production of the ethanol may include diesel fuel burned in the farm tractors, burning of the agricultural waste, production of excess carbon dioxide during fermentation and distillation, and more diesel burned in tanker trucks for distribution. The present invention recognizes that all of these emission sources must be considered before any valid comparison can be made between the ethanol fuel and the baseline fuel it is replacing.
Despite persistent interest and significant progress in using hydrogen as a vehicle fuel, it has not yet become an established alternative fuel, like alcohols, propane or natural gas. The present invention is directed to a system that utilizes a “wells to wheels” approach, for producing, dispensing, using and monitoring a hydrogen enriched fuel. With the system of the invention, a life cycle assessment can compare the total environmental impact associated with the production, transportation and use of the hydrogen enriched fuel, relative to any other baseline fuel.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.